[PATCH 5.10 430/545] sched, cpuset: Fix dl_cpu_busy() panic due to empty cs->cpus_allowed

Greg Kroah-Hartman
2022-08-19T16:42:20Z

From: Waiman Long <longman@redhat.com>

[ Upstream commit b6e8d40d43ae4dec00c8fea2593eeea3114b8f44 ]

With cgroup v2, the cpuset's cpus_allowed mask can be empty indicating
that the cpuset will just use the effective CPUs of its parent. So
cpuset_can_attach() can call task_can_attach() with an empty mask.
This can lead to cpumask_any_and() returns nr_cpu_ids causing the call
to dl_bw_of() to crash due to percpu value access of an out of bound
CPU value. For example:

[80468.182258] BUG: unable to handle page fault for address: ffffffff8b6648b0
:
[80468.191019] RIP: 0010:dl_cpu_busy+0x30/0x2b0
:
[80468.207946] Call Trace:
[80468.208947] cpuset_can_attach+0xa0/0x140
[80468.209953] cgroup_migrate_execute+0x8c/0x490
[80468.210931] cgroup_update_dfl_csses+0x254/0x270
[80468.211898] cgroup_subtree_control_write+0x322/0x400
[80468.212854] kernfs_fop_write_iter+0x11c/0x1b0
[80468.213777] new_sync_write+0x11f/0x1b0
[80468.214689] vfs_write+0x1eb/0x280
[80468.215592] ksys_write+0x5f/0xe0
[80468.216463] do_syscall_64+0x5c/0x80
[80468.224287] entry_SYSCALL_64_after_hwframe+0x44/0xae

Fix that by using effective_cpus instead. For cgroup v1, effective_cpus
is the same as cpus_allowed. For v2, effective_cpus is the real cpumask
to be used by tasks within the cpuset anyway.

Also update task_can_attach()'s 2nd argument name to cs_effective_cpus to
reflect the change. In addition, a check is added to task_can_attach()
to guard against the possibility that cpumask_any_and() may return a
value >= nr_cpu_ids.

Fixes: 7f51412a415d ("sched/deadline: Fix bandwidth check/update when migrating tasks between exclusive cpusets")
Signed-off-by: Waiman Long <longman@redhat.com>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Acked-by: Juri Lelli <juri.lelli@redhat.com>
Link: https://lore.kernel.org/r/20220803015451.2219567-1-longman@redhat.com
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
include/linux/sched.h | 2 +-
kernel/cgroup/cpuset.c | 2 +-
kernel/sched/core.c | 8 +++++---
3 files changed, 7 insertions(+), 5 deletions(-)

diff --git a/include/linux/sched.h b/include/linux/sched.h
index 4bca80c9931f..4e8425c1c560 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -1658,7 +1658,7 @@ current_restore_flags(unsigned long orig_flags, unsigned long flags)
}

extern int cpuset_cpumask_can_shrink(const struct cpumask *cur, const struct cpumask *trial);
-extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_cpus_allowed);
+extern int task_can_attach(struct task_struct *p, const struct cpumask *cs_effective_cpus);
#ifdef CONFIG_SMP
extern void do_set_cpus_allowed(struct task_struct *p, const struct cpumask *new_mask);
extern int set_cpus_allowed_ptr(struct task_struct *p, const struct cpumask *new_mask);
diff --git a/kernel/cgroup/cpuset.c b/kernel/cgroup/cpuset.c
index ec39e123c2a5..c51863b63f93 100644
--- a/kernel/cgroup/cpuset.c
+++ b/kernel/cgroup/cpuset.c
@@ -2162,7 +2162,7 @@ static int cpuset_can_attach(struct cgroup_taskset *tset)
goto out_unlock;

cgroup_taskset_for_each(task, css, tset) {
- ret = task_can_attach(task, cs->cpus_allowed);
+ ret = task_can_attach(task, cs->effective_cpus);
if (ret)
goto out_unlock;
ret = security_task_setscheduler(task);
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 042efabf5378..8765de76a179 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -6586,7 +6586,7 @@ int cpuset_cpumask_can_shrink(const struct cpumask *cur,
}

int task_can_attach(struct task_struct *p,
- const struct cpumask *cs_cpus_allowed)
+ const struct cpumask *cs_effective_cpus)
{
int ret = 0;

@@ -6605,9 +6605,11 @@ int task_can_attach(struct task_struct *p,
}

if (dl_task(p) && !cpumask_intersects(task_rq(p)->rd->span,
- cs_cpus_allowed)) {
- int cpu = cpumask_any_and(cpu_active_mask, cs_cpus_allowed);
+ cs_effective_cpus)) {
+ int cpu = cpumask_any_and(cpu_active_mask, cs_effective_cpus);

+ if (unlikely(cpu >= nr_cpu_ids))
+ return -EINVAL;
ret = dl_cpu_busy(cpu, p);
}

--
2.35.1